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Old 06-29-2016, 01:01 PM   #1
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Make Cherokee Flat Tow mode automatic

I picked up the Flat Tow cable kit from Jeep yesterday $138, but Jeep Care is going to reimburse me (Thank You Kori).
I had suspected that it could have been done automatically instead of a switch and installing a fuse.
And it can be....but you still need to buy/get the flat tow kit because of a CAN bus termination block.

I will summarize what needs to be done now, and then post more detailed info when I actually do the install. If you have some basic electronics knowledge, this post will give you the info you need.

The Electronic Power Steering (EPS) is connected to the CAN bus of the vehicle in addition to getting power when the key is turned on.

The standard Flat Tow kit installs a DPST switch AND a CAN termination block in the console. Throwing the switch, disconnects the EPS from the CAN bus, but also leave it terminated with the proper 120 ohm termination.


There is also a relay which is installed under the hood, which is a SPDT, and simply disconnects the EPS from the ignition power bus, and connects it directly to 12V (this powers up the EPS to prevent the wobble). This relay is activated by installing a fuse.


IF you have the kit already installed by the dealer, you just need to replace the switch with a DPST relay which is energized by the same wire that energizes the relay under the hood.

Finally, remove the fuse connection to the battery of the Tow Relay harness, and connect it to your 12V charge line. There needs to be a blocking diode installed which prevents the toad battery from energizing the relays.

Now, as soon as you connect you electrical tow cable, the TOAD will go into flat tow mode.

If you park overnight, you should unplug the electrical cable to prevent battery drain....BUT, if you have a ignition controlled charge line (like Freightliner), the charge line is only active when the RV ignition is on.

This is a much cleaner approach.

Photos attached of the kit.

Regards,
Dan
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Old 06-29-2016, 03:25 PM   #2
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I'm not too smart with electronics so please be somewhat layman with the details.




Thx,
Steve
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Old 06-29-2016, 04:45 PM   #3
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Here is a schematic of the Installed tow cable to show what FCA has done, AND it has the mods to make it automatic.

As stated, you simply remove the dash switch and replace it with a relay.
Then connect to your charge line under the hood.

Dan
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Old 06-30-2016, 05:11 AM   #4
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The dash-switch you speak about, on my Trailhawk, was installed by dealer inside the console, not on the dash. That seems to be the way the Service Bulletin instructs them to do the kit install. It would be easy to get to if it was on dash or better if it was underhood. I am not sure where those wires go but I know dealer had to remove parts of the console to route the wiring to it. I think the best way to replace that switch would be to find out where it's wiring comes from rather than to disassemble the console. Where do they connect? under hood? under dash?
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Old 06-30-2016, 08:01 AM   #5
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Thanks, Dan. Got the call yesterday that my kit is now at the dealer. Will be about 10 days before we make it back to town, tho.

Thanks for the post,

/ken
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Old 06-30-2016, 08:14 AM   #6
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Quote:
Originally Posted by rpasetto View Post
The dash-switch you speak about, on my Trailhawk, was installed by dealer inside the console, not on the dash. That seems to be the way the Service Bulletin instructs them to do the kit install. It would be easy to get to if it was on dash or better if it was underhood. I am not sure where those wires go but I know dealer had to remove parts of the console to route the wiring to it. I think the best way to replace that switch would be to find out where it's wiring comes from rather than to disassemble the console. Where do they connect? under hood? under dash?
Yes, I should have said Console.
The two connections for the switch are inside the console.
That is where the CAN bus connections are made.
Then you would need to run a power wire from the console up to the other relay under the hood.

You could install another cig lighter socket to fill the hole from the switch.

Dan
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Old 07-06-2016, 07:13 AM   #7
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Quote:
Originally Posted by dpinvidic View Post
Yes, I should have said Console.
The two connections for the switch are inside the console.
That is where the CAN bus connections are made.
Then you would need to run a power wire from the console up to the other relay under the hood.

You could install another cig lighter socket to fill the hole from the switch.

Dan
I've been thinking about your idea and it is quite clever. I'm not trying to be critical here, but I decided not to pursue it.

The small reason is having to run wiring back into that console, but the big reason is what would potentially occur if the charge line from the coach goes out, say by fuse blowing. With your system, the charge line going out would immediately take the Cherokee out of "wobble-mitigate" mode, whereas with the present manually-activated setup the only consequence of the charge line going out would be possible battery discharging after an extended trip.
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Old 07-06-2016, 07:04 PM   #8
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Quote:
Originally Posted by rpasetto View Post
I've been thinking about your idea and it is quite clever. I'm not trying to be critical here, but I decided not to pursue it.

The small reason is having to run wiring back into that console, but the big reason is what would potentially occur if the charge line from the coach goes out, say by fuse blowing. With your system, the charge line going out would immediately take the Cherokee out of "wobble-mitigate" mode, whereas with the present manually-activated setup the only consequence of the charge line going out would be possible battery discharging after an extended trip.
YES, you are correct. However, remember that the wobble does not happen immediately. I towed for several thousand miles before I had my first and only wobble.

If your interested, here are s couple other options.
1. Install a indicator light on the dash or console of the jeep (this is what I had planned) which lights when the relays are energized.
2. If you have a dash mounted AUX brake indicator light, wire it through another relay powered by the charge line. If the charge line was bad, the aux brake indicator would not lite. If that happened, you would have two thing to check.

All of these are trade-offs between convenience and needs.

Remember the error codes created when the key is turned on and still in tow mode will reset after a couple of ignition cycles.

Regards,

Dan
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Old 07-15-2016, 11:19 PM   #9
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Under Hood Installation Report

Tonight I installed the under hood relay that comes with the Flat Tow kit.

I did not have to make any modifications to this part, other than connecting the 12V supply to directly to my charge line (which contains a blocking diode). A blocking diode is needed so the relay does not get energized by the TOAD's battery. The fuse is NOT removed from the fuse holder.

This is actually a easy way to eliminate dealing with the fuse. You can still leaft the console mounted switch in-place if you desire.

The installation is pretty easy, and they give good instructions.
As shown in a earlier post, all this relay does is intercept the power lead for the EPS, and then in tow mode connects it to 12V.

NOTE: the fuse in the fuse box for this #30 is marked ECM, EPS, Fuel pump. So these items will be getting powered up in tow mode.

Here are pictures, and I will do the interior install tomorrow.
Car drove fine tonight after this mod.

Regards,

Dan
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Old 07-16-2016, 08:50 PM   #10
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Inside Relay install

Finished the inside work installing the relay in the console.
Again, the instructions were pretty good.

I added a indicator light on the console which is one when the inside relay is on. This indicates TOW MODE.

Pretty happy with this, it is completely automatic.
My Freightliner chassis has a "switched" battery charge line, so the Jeep is only in tow mode when the RV is running.


Another mod I made was to remove the termination resistors from the new CAN block, and use it only as a connection block. Then, I added a 120 ohm resistor across the "spare" relay contacts so that in TOW mode the CAN bus from the EPS is isolated from the car, but still terminated. I preferred not to allow a termination resistor in the middle of the bus..

Here are the final pics.

Regards,

Dan
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Old 07-16-2016, 09:12 PM   #11
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Inside Relay install

Finished the inside work installing the relay in the console.
Again, the instructions were pretty good.

I added a indicator light on the console which is one when the inside relay is on. This indicates TOW MODE.

Pretty happy with this, it is completely automatic.
My Freightliner chassis has a "switched" batery charge line, so the Jeep is only in tow mode when the RV is running.


Another mod I made was to remove the termination resistors from the new CNA block, and use it only as a connection block. Then, I added a 120 ohm resistor acorss the "spare" relay contacts so that in TOW mode the CAN bus from the EPS is isolated from the car, but still terminated. I preferred not to allow a termination resistor in the middle of the bus..

Here are the final pics.

Regards,

Dan
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Old 08-14-2016, 06:59 PM   #12
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First trip report....Great Success

Just got back from our first trip using the Automatic Mode switching arrangement.

It was great....basically there is nothing special that needs to be done, other than be sure to connect the electrical tow cable AFTER the jeep transfer case is in neutral. ANd disconnect the cable before switching the transfer case into gear.

After I connect the cable, I take a peek at the indicator light on the console to confirm everything is powered up..

We had a wrong turn incident on our way home, and I needed to unhook the toad to get the RV tuned around. I really appreciated not having to mess with a under hood fuse during this process.

Even if you don't think that the fuse and switch are a nuisance, you really should make this conversion....because I will bet big money that you will eventually forget either the fuse or the switch and end up with a check engine light...

Regards,

Dan
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Old 08-15-2016, 07:18 AM   #13
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Quote:
Originally Posted by dpinvidic View Post
Just got back from our first trip using the Automatic Mode switching arrangement.

It was great....basically there is nothing special that needs to be done, other than be sure to connect the electrical tow cable AFTER the jeep transfer case is in neutral. ANd disconnect the cable before switching the transfer case into gear.

After I connect the cable, I take a peek at the indicator light on the console to confirm everything is powered up..

We had a wrong turn incident on our way home, and I needed to unhook the toad to get the RV tuned around. I really appreciated not having to mess with a under hood fuse during this process.

Even if you don't think that the fuse and switch are a nuisance, you really should make this conversion....because I will bet big money that you will eventually forget either the fuse or the switch and end up with a check engine light...

Regards,

Dan
Quick run this thru the Patent Office and then charge FCA for the rights to use it.
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